1. Related Application(s)
In order to more fully appreciate the significance of the instant invention, related co-pending U.S. patent application Ser. No. 385,176, filed June 4, 1982, now U.S. Pat. No. 4,500,264, on behalf of George H. Lindner should be carefully reviewed.
2. Field of the Invention
The present invention relates generally to air operated, positive displacement diaphragm pumps that are submerged in the liquid to be discharged, and more particularly to diaphragm pumps employing a plurality of displacer valves.
3. Prior Art
Diverse diaphragm pumps have been used in the prior art to withdraw liquid from a receptacle through an inlet port and discharge same through an outlet port. The diaphragm usually divides the pump housing into a supply chamber and a pressure chamber. A first check valve regulates flow into the supply chamber, and a second check valve controls the flow therefrom. Electrical or hydraulic signals are supplied to an externally situated operator, such as a piston, for controlling the movement of a diaphragm or membrane within the pump casing. The movement of the diaphragm forces the pressurized fluid out of the supply chamber and past the second check valve. Representative reciprocating diaphragm pumps are shown in U.S. Pat. No. 3,285,182, granted Nov. 15, 1966 to H. E. Pinkerton, U.S. Pat. No. 3,814,548, granted June 4, 1974 to Warren E. Rupp, and U.S. Pat. No. 4,021,164, granted May 3, 1977 to Hans Peter Tell.
Known reciprocating diaphragm pumps of low capacity, however, have very little, if any, self-priming action. Such pumps therefore must be kept at a level close to, or below, the liquid level of the container from which the liquid is being pumped. Also, check valves of known reciprocating pumps exhibit a tendency to leak. While the leakage is a minor problem when relatively large quantities of liquid are being pumped, the problem assumes far greater importance when the quantities being pumped are but a few milliliters over an extended period of time and when exact metering is required.
The first of the aforementioned shortcomings of known reciprocating diaphragm pumps was remedied by the diaphragm pump, shown in detail in FIGS. 2-5 of aforementioned, co-pending patent application Ser. No. 385,176, U.S. Pat. No. 4,500,264. To illustrate, the diaphragm pump shown and described in the co-pending application responds to control pulses of low pressure air delivered from a pulse generator controlled by pneumatic logic circuitry; the low pressure air is readily available in industrial plants and represents a marked cost saving over known electrical and hydraulic control systems. Also, the driving membrane, pumping membrane, and displacer of the co-pending application function effectively to discharge small quantities of liquid at a selected rate; by manipulation of a resistor in the logic circuitry, the rate can be varied. Additionally, the diaphragm pump of the co-pending application can be submerged in the liquid to be discharged, even a corrosive liquid, and function satisfactorily over extended periods of time and with constant, reproducible discharge rates.
While the diaphragm pump of the aforesaid co-pending application represents a significant advance over known diaphragm pumps, extensive field tests of said pump, while handling corrosive liquids such as tin compounds for hot coating glass bottles, suggested even further refinements in the pump design would be desirable. For example, the instant diaphragm pump obviates the use of an inlet check valve and an outlet check valve, replacing such valves by a pair of positively driven displacer valves. The pair of positively driven valves, when coupled with the conventional positively driven diaphragm valve, coact to force a metered amount of corrosive liquid through the pump body in a sequence of steps. The concept of the three positively driven displacer valves used in the instant diaphragm pump can be extended to four or more displacer valves, as desired or as needed, for successful low volume operation.
Additionally, the instant positive displacement diaphragm pump can be controlled by a pneumatic pulse generator comprising a logic circuit of simplified design. The instant positive displacement diaphragm pump is compatible with the logic circuit shown in FIG. 6 of co-pending application Ser. No. 385,176, U.S. Pat. No. 4,500,264, an can function in concert with other pneumatic and pure-fluid logic circuits with equal facility.